The Hidden Engineering of Wildlife Crossings — Practical Engineering

Quick Overview

Wildlife crossings, including the Wallace Annenberg Wildlife Crossing, are large-scale infrastructure projects designed to mitigate the severe ecological and economic impacts of roads on animal populations. These crossings, which can be overpasses or underpasses, are engineered to facilitate safe animal movement, reducing wildlife-vehicle collisions that cause billions in damages and hundreds of human fatalities annually, while also combating habitat fragmentation and genetic isolation in species like mountain lions.

Key Points: The Wallace Annenberg Wildlife Crossing, under construction over the 101 Freeway in Los Angeles, will be the world's largest wildlife crossing, costing $92 million. Roads cause over 1,000,000 wildlife-vehicle collisions annually in the U.S., leading to tens of thousands of human injuries, hundreds of fatalities, and over $8 billion in damages. Wildlife crossings are designed to accommodate different animal behaviors, including non-responders, pavers, avoiders, and speeders, with specific features like fencing and light considerations. Overpasses, like ecoducts and land bridges, are often the most effective for larger animals, blending into the landscape with native vegetation and providing clear sightlines. Underpasses, such as culverts and existing bridge structures, can also be utilized, sometimes requiring manual animal transport for species like amphibians. Habitat fragmentation caused by roads severely impacts migratory species and can lead to genetic isolation, as observed in Southern California cougar populations. Increased federal funding and advanced engineering guidance are driving the construction of more wildlife crossings, aiming to improve safety and ecological health.

Context: Roads, while essential for human transportation, significantly impact wildlife populations and ecosystems. These impacts range from direct mortality through vehicle collisions to habitat fragmentation, which isolates animal populations and reduces genetic diversity. Recognizing these severe consequences, engineers and ecologists are collaborating to design and implement specialized infrastructure solutions known as wildlife crossings.